1. Field of the Invention
The present invention relates to a non-halogen flame-retardant resin composition, which does not generate halogen gas during combustion, demonstrates high flame-retardancy, and excels in safety for the environment.
2. Description of the Related Art
As thermoplastic resins are flammable, various technologies to confer flame-retardancy have been proposed for applications that require flame-retardancy. As is known, flame-retardant formulations mixing a halogen-based flame-retardant agent such as a bromine compound and antimony oxide, which excel in flame-retardancy, with a thermoplastic resin, have been used as such technique. Halogen-based flame-retardant agents exert excellent flame-retardant effect by radical trapping activity, halogen gas (incombustible gas) generation, and the like. However, as this halogen gas is harmful to organisms, as is a recent issue, emergence of flame-retardant resin compositions with non-halogen formulations is strongly desired.
Various technologies using metal hydroxides, such as, magnesium hydroxide, have been proposed in recent years as flame-retardant formulations of thermoplastic resins used in the manufacture of coating insulators for electric wires/cables and sheets. Metal hydroxides have an advantage of low toxicity, small amount of smoke generation, and low corrosiveness, and exert flame-retardant action by releasing crystalization water at combustion time.
However, as this flame-retardant effect is not strong, for instance, when the base resin, which is the target of the addition, is polyolefin, even if, with respect to 100 parts by mass of polyolefin, an equal amount of 100 parts by mass is mixed, the oxygen index, which is one of the indicators of material combustibility (flammability), demonstrates a number of only 30 or less.
Flame-retardant resin compositions mixing, for instance, a metal hydroxide that has been surface treated with a surface treatment agent, such as, a silane coupling agent, with a thermoplastic resin, are known as flame-retardancy technologies for thermoplastic resins using metal hydroxides (see Japanese Patent Publication No. 2825500, Japanese Patent Publication No. 3019225 and Japanese Patent Publication No. 3072746).
However, merely mixing a surface treated metal hydroxide with a thermoplastic resin leaves a low and insufficient oxygen index, such that, in order to confer the thermoplastic resin with sufficient flame-retardancy, it is necessary to mix a metal hydroxide in large amounts.
In addition, flame-retardant resin compositions by admixing of a metal hydroxide and an organopolysiloxane with a thermoplastic resin have been reported (see Japanese Patent Examined Publication No. H7-119324, Japanese Patent Publication No. 3051211, Japanese Patent Publication No. 3063759 and Japanese Patent Application Laid-open No. H4-226551) as flame-retardancy technologies other than those described above. Although flame-retardancy increases when a metal hydroxide and an organopolysiloxane are used in combination, in order to allow compliance with various flame-retardancy regulations, a flame-retardant formulation exerting still higher flame-retardancy is necessary.
In addition, recently, non-halogen flame-retardant resin compositions mixing a metal hydroxide, an organopolysiloxane and an additive with a thermoplastic resin have been reported (see Japanese Patent Application Laid-open No. 2004-250676 and Japanese Patent Application Laid-open No. 2003-128939). Although it is clear that these flame-retardant resin compositions have increased flame-retardancy with an oxygen index showing values of 48 or higher, the flame-retardancy is still insufficient to pass UL-94 and UL-VW1 test standards.
In addition, a non-halogen flame-retardant resin composition mixing a metal hydroxide, a highly polymerized organopolysiloxane, an organopolysiloxane containing an unsaturated functional group, and a radical generating agent, with a thermoplastic resin, has been reported (Japanese Patent Application Laid-open No. 2003-034755).
Although this non-halogen flame-retardant resin composition is imparted with enough flame-retardancy to pass VW-1, as it must be crosslinked with a peroxide, not only manufacturing becomes laborious due to its low flowability, it has problems in terms of moldability.